Ring fan and shroud air guide system

ABSTRACT

A ring fan and shroud guide system which includes a rotating fan member with a conical outer ring and a cylindrical shroud member overlapping at least a portion of the outer ring. A plurality of guide vanes are provided in the shroud which minimize the tangential velocity component of the air flow entering the tip-gap region and provide improved air flow through the system. The guide vanes can have a curved configuration.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is continuation of U.S. application Ser. No. 12/594,017, filed Sep.30, 2009.

TECHNICAL FIELD

The present invention relates generally to a ring fan and shroudassembly and more particularly to a ring fan and shroud assembly withimproved air flow characteristics.

BACKGROUND OF THE INVENTION

Axial type fans move air, or other fluids, using rotating impellerblades. As the impeller blades rotate, different pressures on oppositesides of the blades are developed. The discharge sides of the impellerblades typically develop a high pressure while the intake sides developa low pressure. The pressure differential between these two sides causesthe fluid to flow from the high-pressure discharge side to thelow-pressure intake side near the tips of the impeller blades creatingan undesirable back flow of some of the fluid flow passing through thefan. It is well-known that this backflow can decrease the efficiency ofthe fan and may lead to undesirable noise generation.

Engine cooling fans develop static pressure across the fan such that theregions ahead of the fan are at significantly lower pressure thanregions behind the fan. Many engine cooling fans have cowlings orshrouds positioned circumferentially around them in order to assist indirecting the air flow in the desired direction. Practical operation offans used in motor vehicle cooling systems dictate minimum clearancesbetween the rotating fan members and stationary shroud members in orderto ensure safe, durable functioning throughout the life of the vehicle.

Many of the cooling fan members used in such systems are ring-type fans,i.e. the fans have a circumferential ring member positioned on the tipsof the fan blades. The pressures developed across the cooling fans driveleakage flow through the gaps occurring between the fan's blade tips orany rotating ring, and the stationary surfaces of the shroud.

In ring fans, the leakage flow encounters the tip gap at the trailingedge of the rotating ring and enters the gap region having a very hightangential velocity component. As the leakage flow progresses throughthe gap region, the viscous drag of the rotating ring continues tostrengthen this vortical flow until finally it reaches the exit of thegap region, which is just upstream of the tips of the blades of the fan.

When the recirculating leakage flow reenters the main fan air flowpassage, it possesses a very high tangential component, which is at oddswith the velocity and direction of the primary incoming air flow of thefan. As the tangentially-oriented recirculating flow mixes with thepassage of the primary air flow which is mostly axial, a vortex isformed adjacent the front of the leading edge at the tips of the fanblades. Since the leading edges of fan blades are designed for theprimary flow velocity condition, the vortex encountered by the blades ismisaligned relative to the intended inlet vector. This can cause the tipregion to stall and the resulting low relative-momentum flow can “hangup” in the region of the blade tips and fan ring. This reduces the airflow rate of the fan, as well as its static pressure, and also increasesthe drag.

It would therefore be desirable to have a ring fan and shroud assemblythat was effective in reducing these complications. It would further bedesirable to minimize or eliminate the tangential velocity componentprior to reinducing the leakage flow back into the primary air streamflowing through the fan. It would further be desirable to minimize thetip gap leakage flow and prevent tip stall.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a ringfan and shroud assembly which minimizes the tip gap leakage flow andprevents tip stall. It is a further object of the present invention toprovide a ring fan and shroud assembly with improved efficiency andreduced noise generation.

It is an additional object of the present invention to provide a ringfan and shroud assembly in which the shroud and guide vanes can beeasily formed in a conventional two-piece mold injection molding process

In accordance with the objects of the present invention, a ring fan andshroud guide assembly is provided. The fan assembly includes a pluralityof impeller blades positioned within and attached to a conical outerring. A portion of the stationary shroud member can overlap radiallyinwardly a portion of the fan's rotating ring. The shroud member andring member form an annular recirculation nozzle adjacent the primaryinlet air flow passage of the fan. A plurality of curved guide vanes areprovided in the shroud member which act on the back flow of air enteringthe tip gap. The axially extending guide vanes have a substantiallytangential leading edge orientation which align with the air flowentering the air gap. The curved guide vanes minimize or eliminate thetangential velocity component of the back flow air stream prior toreinducing that leakage flow back into the air stream through therecirculation nozzle.

The tip-gap has an entrance area substantially larger than the area ofthe recirculation nozzle. This, together with a converging exit regionincreases the velocity of the air flow injection of the leakage flowback into the fan's air stream.

Other features, benefits and advantages of the present invention willbecome apparent from the following description of the invention, whenviewed in accordance with the attached drawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a vehicle engine having a cooling systemaccording to a preferred embodiment of the present invention.

FIG. 2 illustrates a fan assembly in accordance with a preferredembodiment of the present invention.

FIG. 3 illustrates a shroud member in accordance with a preferredembodiment of the present invention.

FIG. 4 shows a ring fan and shroud assembly in accordance with apreferred embodiment of the present invention.

FIG. 5 is a cross-sectional view of the ring fan and shroud assembly asshown in FIG. 4, the cross-section being taken along lines 5-5 in FIG.4.

FIG. 6 is an enlarged view of a portion of the ring fan and shroudassembly cross-section as shown in FIG. 5.

FIG. 7 is an illustration similar to FIG. 6 and showing the componentsand air flows in a schematic manner.

FIGS. 8 and 9 illustrate an embodiment of the guide vanes in accordancewith the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates a ring fan and shroud guide system 10 in accordancewith the present invention. Although it is contemplated that the ringfan and shroud guide assembly 10 can be used in a variety ofapplications, the system 10 in one preferred embodiment is intended foruse in a cooling system for an engine 11. Specifically, the preferredembodiment of the present invention is intended for use in conjunctionwith a radiator cooling system in a truck or large vehicle. It is to beunderstood, however, that the present invention can be used in manyapplications, and the invention is not to be limited only to trucks orother vehicles.

The fan member 15 has a central hub member 13 and a plurality of blademembers 12 (also called “impeller” members). A circumferential ringmember 14 is positioned at and connected to the ends (or tips) of theblade members. The use of impeller blades and a rotating ring element toform a fan assembly is well known in the art, and these fan assembliesare commonly referred to as ring fans.

Also, although in the preferred embodiments, the ring fan is a solidcomplete annular ring member and is positioned at the tips of theblades, it is also possible that the ring member can be discontinuouswith gaps between the blades or have openings in the ring itself, orthat the ring member (or discontinuous portions thereof) can bepositioned radially inwardly slightly from the ends of the blades.

The ring member 14 is preferably intricately formed with the fanassembly and thus fixedly attached to the tips of the fan blades. Inaccordance with a preferred embodiment of the present invention, thering member also has a conical shape, as shown in the drawings. Theouter ring has a smaller diameter at the air inlet or low pressure side16 of the fan assembly and a larger diameter at the air discharge side,or high pressure side 17 of the rotating fan member.

The shroud member 20 is cylindrical in shape and is positionedcircumferentially around, or substantially circumferentially around, allor a principal portion of the rotating ring fan member.

The shroud member also has a portion or component 22 which is positionedradially inwardly of the leading edge 24 of the ring member and axiallyoverlaps a corresponding portion 26 of the ring member. The portion 26is spaced a radial distance D-1 from the ring member and forms a nozzle30 with an annular cross-sectional area. This nozzle 30 is called therecirculation nozzle as it reinjects into the primary fan air stream 32the back flow of air 34 which enters into the tip gap 36.

The trailing edge 38 of the ring member and a second portion or surface40 of the shroud member are spaced apart a certain radial distance D-2.This is called the tip gap 36—or tip gap region—and is the area where aportion of the air flow (see arrows 34 in FIG. 7) flows back in theopposite direction of the main air flow of the fan 15. The tip gapregion also has an annular cross-sectional area.

The distance D-2 is larger than the distance D-1, and similarly theannular cross-sectional area of the tip gap region 36 is larger than theannular cross-sectional area of the recirculation nozzle 30. Preferably,the distance D-2 is substantially larger than distance D-1, by 50% ormore.

A plurality of guide vanes 42 are provided in the shroud member 20. Thespace inbetween the vane members may be varied to modify frequency ofpressure pulses relative to a point on the fan as it proceeds through afull revolution in an effort to reduce fan noise and vibration (NVH).The number of vanes—as well as the number of fan blades—also preferablycorrespond with a prime numbering system in order to help reduce NVH. Inthis regard, one possible ring fan and shroud assembly can have thirteenfan blade members and thirty-one guide vane members.

As indicated, in accordance with the present invention, the shroudmember forms a recirculation nozzle which defines a flow passageadjacent to the primary incoming flow stream. The larger entrance areaof the tip-gap region in conjunction with a converging exit region ofthe area of the recirculation nozzle effectively provides high velocityinjection of the leakage air flow back into the fan air stream. Thisalso minimizes the tip-gap leakage flow. The tip-gap leakage flow 50 andthe upstream primary flow 32 are merged together and align with eachother as shown in FIG. 7. This is in proper incidence with respect tothe leading edge angle of the tip of the fan blade near the ring.

Also, the high velocity leakage flow that reenters the fan's tip airstream through the reduced area in the nozzle utilizes the Coanda effectto stay attached to the rotating ring member. This helps to energize thelow relative momentum flow existing in the blade tip/rotating ringregion and prevents tip stall.

The guide vanes 42 preferably have a curved configuration. As shown inFIG. 8, the vanes also have substantially tangential leading edges 62which initially direct and orientates the air flow entering the tip-gapregion, and have substantially radial trailing edges 60 adjacent therecirculation nozzles. The guide vanes minimize or eliminate thetangential velocity component of the air flow as it passes through theshroud chambers—and prior to reinducing the leakage flow back into theair stream flowing into the fan.

It is also possible for the shroud to have guide vanes which havedifferent configurations, so long as some are curved and the pattern ofvarious types and configurations is uniformly spaced around thecircumference of the shroud for balance. The amount of curvature of theguide vanes could even differ around the perimeter of the shroud.

The guide vanes on the shroud member smoothly “capture” the leakage flowas it enters the tip gap region. This is aided by the substantialtangential leading edge of the vanes, along with the substantiallyradial trailing edge. This gently turns the flow direction fromtangential to radial and axial. A meridional air flow is created as thevanes effectively remove the tangential component from the recirculationflow. A meridional air flow is one having only radial and axial velocitycomponents without a tangential component present.

The reinjection of the recirculation flow at high velocity energizes thelow relative momentum fluid and utilizes the Coanda effect to help keepthe primary flow attached to the surface of the rotating ring. TheCoanda effect is a well-known aerodynamic effect discovered in 1930 byHenri-Marie Coanda. Coanda observed that a stream of air emerging from anozzle tends to follow a nearby surface as long as the curvature orangle of the surface does not vary sharply from the flow direction. Thepresent invention uses this effect since the flow emerging from therecirculation nozzle is directed along the inner surface of the rotatingring, helping to prevent tip stall. Additionally, in one embodiment, airflows past the discharge surface and along the shroud exit surfacewithout recirculating back through the tip gap.

In one embodiment, the shroud exit element is substantially parallel andcoincident with the trailing edge of the rotating ring. The decrease inflow area between the tip gap region entrance and exit, and theconverging nature of the nozzle promote acceleration of the flow as itreenters the fan passage. This promotes a significant pressure dropacross the nozzle which in turn improves the capacity of the fan tosustain high static pressure differential across the fan.

In a preferred embodiment of the present invention, the shroud guidevane members are characterized by the following features: the tip-gapD-2 ranges from ¼ inch to 1 inch, the inlet angle A ranges from 0 to 20degrees, and the exit angle B ranges from −20 degrees to +20 degrees.See FIGS. 8-9.

In addition, the recirculation nozzle 30 formed by the present inventioncan be characterized by the following features in accordance with apreferred embodiment: The nozzle gap D-1 ranges from ⅛ inch to ½ inch,the overlap 24 of the shroud at the nozzle ranges from 0.1 to 1 inch,and the nozzle angle C of the nozzle exit edge ranges from 0 to 20degrees.

With the present invention, a significantly improved pressure rise isachieved, together with stability and static efficiency. In general, thelow relative momentum fluid trapped under the inside of the ring memberat the blade tips is energized and the recirculation flow is reinjectedback into the flow passage with the swirl removed. This helps to movethe flow through the blade tip region and ensure that the recirculatingflow encounters the leading edges of the blades aligned with the inletangle of the blades.

The ring fan and shroud guide system in accordance with the presentinvention can be manufactured using a two-piece injection molding tool.It is not necessary in accordance with the present invention to utilizeexpensively machined channels in the casing walls as apparently employedin some current compressor tip casing treatments.

While preferred embodiments of the present invention have been shown anddescribed herein, numerous variations and alternative embodiments willoccur to those skilled in the art. Accordingly, it is intended that theinvention is not limited to the preferred embodiments described hereinbut instead limited to the terms of the appended claims.

What is claimed is:
 1. A ring fan and shroud air guide systemcomprising: a fan member having a hub and a plurality of bladesextending outwardly from the hub; a ring member attached to the blades,said ring member having a conical axially extending shape; a shroudmember positioned around said fan member and ring member, said shroudmember having a portion axially overlapping and radially inward of afirst portion said ring member and forming a tip gap with a secondportion of said ring member; and a plurality of guide vanes positionedin said shroud member, said guide vanes having a configuration tominimize the tangential component of the recirculation air flow throughsaid tip gap.
 2. A ring fan assembly comprising: a fan having a hub witha plurality of projecting fan blades and an outer ring member; arecirculating flow element generally forward adjacent said outer ringmember; a plurality of guide vanes positioned within said recirculatingflow element having an inlet angle nearly tangential with an outer entrydiameter radial surface of said recirculating flow element and having anoutlet angle nearly radial along an inner exit diameter surface of saidrecirculating flow element.
 3. A ring fan assembly as described in claim2 wherein said inlet angle is generally 20° or less.
 4. A ring fanassembly as described in claim 2 wherein said outlet angle is generallyplus or minus radial 20° or less.
 5. A fan assembly as described inclaim 2 wherein there are a prime number of said guide vanes.
 6. A fanassembly as described in claim 2 wherein the spacing between at leasttwo of said vanes is not equal to the spacing between two other saidguide vanes.
 7. A ring fan assembly as described in claim 2 wherein saidrecirculating flow element forms an inlet nozzle for said ring fanassembly.
 8. A ring fan assembly as described in claim 2 wherein saidguide vanes are integrally molded with said recirculating flow element.9. A ring fan assembly as described in claim 8 wherein said guide vanesare fabricated from a polymeric material.
 10. A ring fan assembly asdescribed in claim 2 wherein said guide vanes are molded and whereinsaid guide vanes have linearly extruded surfaces.
 11. A ring fanassembly as described in claim 2 wherein said guide vanescircumferentially angularly decrease in space therebetween from inlet tooutlet.
 12. A ring fan assembly as described in claim 2 wherein saidrecirculating flow element comprises a shroud member, said shroud memberhaving an exit element substantially parallel or coincident with the airflow being ejected from trailing edges.
 13. A ring fan assembly asdescribed in claim 2 wherein said recirculating flow element is acomponent of an outer shroud member.
 14. A ring fan assembly asdescribed in claim 13 wherein said recirculating flow element is angledfrom said outer shroud member.
 15. A ring fan assembly as described inclaim 2 wherein the inner diameter of said recirculating flow element isdimensionally radially inward and axially forward of said ring member.16. A fan assembly as described in claim 2 wherein said guide vanes havea curvilinear shape.
 17. A ring fan assembly comprising: a fan having ahub with a plurality of projecting fan blades and an outer ring member;a recirculating flow member generally axially forward adjacent said ringmember, said recirculating flow element having outer entry and innerexit diameters radially dimensionally juxtaposed by an outer diameter ofsaid ring member; and a plurality of curvilinear guide vanes with linearextruded surfaces positioned within said recirculating element having aninlet angle generally 20° or less tangential with an outer diametersurface of said recirculating element and having an outlet anglegenerally 20° plus or minus radial along an inner diameter surface ofsaid recirculating flow element.
 18. A ring fan assembly comprising: afan having a hub with a plurality of projecting fan blades, and an outerring member; a recirculating flow member generally axially forwardadjacent said ring member, an inner diameter of said recirculatingelement being greater than an outer diameter of said ring member; and aplurality of curvilinear guide vanes positioned within saidrecirculating flow element having an inlet angle generally 20° or lesswith an outer entry diameter surface of said recirculating element andhaving an outlet angle generally plus or minus 20° radial along an innerdiameter surface of said recirculating flow element.